Elastic nonwoven fabrics made from thermoplastic polyurethane elastomers (hereinafter “TPU”) proposed so far have been used in applications including garments, hygiene materials and materials for sporting goods due to their high elasticity, low residual strain and superior breathability.
JP-A-2002-522653 addresses the characteristic “sticky” nature of the thermoplastic elastomers as one of the problems encountered in spunbonding the elastomers into nonwoven fabrics. It has been pointed out that turbulence in the air can bring filaments into contact and they can adhere to one another in the spunbonding. The “stickiness” has been proven to be especially troublesome during rolling up of the webs. Further, JP-A-2002-522653 mentions breakage and elastic failure of the strand during extrusion and/or stretching.
These problems are solved by a strand that comprises at least two polymers, one is more elastic than the other, with the less elastic polymer constituting at least a portion of the peripheral surface of the strand. Specifically, Example 10 of JP-A-2002-522653 demonstrates production of a spunbonded web using TPU to constitute the core of filament and a liner low-density polyethylene (hereinafter “LLDPE”) to constitute the sheath. It is read, “the bonded web became manageable and could be wound up and subsequently unwound”. However, if fibers become thin in the above production, filament breaking occurs so that attempts to obtain nonwoven fabrics having desired fiber diameters will fail.
JP-A-9-291454 discloses elastic nonwoven fabrics, having excellent drape, comprising a conjugate fiber comprising a crystalline polypropylene and a thermoplastic elastomer. It discloses an elastic nonwoven fabric which comprises a concentric sheath-core conjugate fiber made up of 50 wt % of a urethane elastomer as the core and 50 wt % of a polypropylene as the sheath (Example 6). The disclosure extends to an elastic nonwoven fabric which comprises a conjugate fiber made up of 50 wt % of a urethane elastomer and 50 wt % of a polypropylene to show a six-segmented cross section (Example 8). These nonwoven fabrics are capable of about 75% elastic recovery after 20% elongation and have excellent drape. However, they are still insufficient in elastic properties for applications such as garments, hygiene materials and materials for sporting goods.
JP-A-2002-242069 discloses nonwoven fabrics comprising a mixture of two kinds of fibers made from two different polymers. It is described that such nonwoven fabrics have superior touch and elastic properties attributed to combined characteristics of the different materials. However, it does not provide a specific disclosure on polyurethane elastomers. As Comparative Example 4 in this specification will illustrate, inferior elastic properties, rough touch and in addition bad spinnability are encountered even when the nonwoven fabrics are produced from a fiber mixture containing a polyurethane elastomer fiber and a polypropylene fiber.